1. Field of the Invention
The invention relates to a polyvinyl chloride formulation useful to insulate automotive primary cables, characterized in that it is lead free, abrasion resistant for use in insulation and sheathing of thin-walled minimum thickness automotive cables able to operate at working temperatures of 105xc2x0 C.
2. Description of the State of the Art
Polyvinyl chloride, xe2x80x9cPVCxe2x80x9d, is used extensively in electrical cables isolation and sheathing because it is economical and easily available, because of its mechanical properties, chemical and weather resistance as well as because of its dielectric properties.
However, in order to obtain some specially required characteristics, it is necessary to investigate new additives producing the desired effect.
With regard to the object of the instant invention PVC is always used in formulations through the addition of plasticizers to remove its natural stiffness and to give it flexibility as well as through the addition of other additives such as thermal stabilizers, lubricants, pigments, loads, impact modifiers as well as flame retardant agents that are added to the compound to obtain the PVC with the desired properties.
PVC itself is a thermally unstable polymer, with decomposition at a temperature of 150xc2x0 C., releasing HCl, producing establishment sites in the polymer which causes the chain crosslinking and its eventual rupture resulting in the degradation of the polymer properties. As PVC decomposes, the resin changes color and becomes stiff and fragile.
To obtain the thermal stability necessary for its processing, PVC compounds always use stabilizers. The most common stabilizers are generally metals salts of organic or inorganic acids and phenols, organometallics, epoxy compounds and phosphites. In the case of compounds used for automotive primary cable insulation, Volkswagen 603 06 specification (December 1999 draft) mentions that the compounds used for thin-walled cable manufacturing should be lead free.
The automotive industry is and will be affected by the following factors:
a). environment regulation forcing companies manufacturing automobiles to diminish the environmental impact of the vehicles both with regard to their emissions and their construction.
b). increase in economy, safety, luxury and comfort offered by the current vehicles.
Said new requirements have forced vehicle manufacturers to carry out modifications and/or reductions both with regard to fuel consumption and the materials used in the manufacturing of the vehicles and their performance.
One of the modifications was reflected in automotive primary cables insulation through the elimination of the noxious materials found in the polymers, among them PVC, that have traditionally use lead because of electrical and cost advantages.
Besides, smaller vehicles have been designed and thus space in the different compartments has been reduced, providing less room for devices, among them for electrical connection harnesses for the connection and signaling of the equipment, said equipment being now more complex because of safety and luxury development in the car industry. For this reason, auto manufacturers have modified cable designs, diminishing the insulation wall thickness in order to reduce weight and diameter without lowering their mechanical resistant, offering thus an alternative for the numerical increase of the circuits currently required by automobiles.
Some isolated technologies are known which partially fulfill the characteristics required, either in the insulation composition or in the way the wires are manufactured or in the disposition of cable construction such as, for example: U.S. Pat. No. 5,326,638, issued to Mottine, Jr et al. relates to the sheathing of insulated communication cables with lead free PVC compositions and a metal antioxidant deactivator system in order to prevent the formation of calcium and zinc chloride affecting the electrical properties.
U.S. Pat. No. 5,149,917 issued to Sawada et al, protects conductors for automotive harness in which the conductors are compressed to reduce the total diameter of the cable, said cables are insulated with different vinyl chloride, crosslinked vinyl or crosslinked polyethylene compositions.
U.S. Pat. No. 4,734,545 issued to Susuki et al., protects compressed conductors for automotive harness insulated with thermoplastic polyurethane, providing abrasion strength.
The first above mentioned invention relates to a communication cable and the two other inventions relates to conductors used in the automotive industry that include polyurethane which promotes abrasion strength but is expensive.